1. Field of the Invention
The present invention relates generally to code division multiple access (CDMA) networks, and specifically to load sharing within a CDMA2000 network.
2. Description of Related Art
High Data Rate (HDR) is a technology originally developed for dedicated packet data applications to meet the increasing demand for wireless Internet Protocol (IP) connectivity with high spectral efficiency. Voice transmissions require low data rates, but maintain stringent delay and jitter requirements. Packet data transmissions, on the other hand, typically require bursty high data rates, with less stringent delay and jitter requirements. The HDR principle is to separate high-speed data completely from the voice network, so that the packet data requirements can be fulfilled optimally and independently.
In May 2000, the CDMA Development Group (CDG) accepted HDR as the 1× Evaluation Phase One: Data Only (1×Ev DO or 1×EV Phase 1), with minor requirements for improvements. Within the 1×Ev DO network, an HDR base station, whether a stand-alone node or integrated within a voice base station, operates on a 1.25 MHZ carrier that is allocated for packet data only.
The HDR base station further employs a single shared, time division multiplexed (TDM) forward link, where only a single terminal is served at any instance. The forward link throughput rate is shared by all HDR mobile terminals. A mobile terminal selects a serving sector (or cell) of the base station by pointing its Data Rate Control (DRC) to the sector and requesting a forward data rate according to the channel condition (i.e., based on the Carrier to Interference (C/I) ratio of the channel).
A multi-user scheduler at the HDR base station is responsible for granting actual data rates to each mobile terminal. The multi-user scheduler within the HDR base station “fairly” distributes the throughput rate for all mobile terminals pointing their DRC's on the same sector. However, each mobile terminal's data through rate is relative to the number of other mobile terminals and the throughput rate of the other mobile terminals. Since a mobile is blind to the amount of traffic in its sector and adjacent sectors, the consequence is that some sectors may be heavily loaded and others may be under loaded.
Previous load sharing methods require the network to select another sector or cell for handoff of one or more subscribers. For example, in PCT Application WO 97/44925, which is hereby incorporated by reference, when a load threshold is exceeded, the network directs a mobile terminal to another cell by channel allocation. As another example, in PCT Application WO 96/38011, which is hereby incorporated by reference, mobile terminals are off-loaded to an alternate sector of the base station when a current sector of the base station becomes loaded beyond a loading threshold.
However, in the CDMA2000 network, handoffs to other sectors or other HDR base stations are not initiated by the network. Instead, in the CDMA2000 network, “virtual” handoffs are performed by the mobile terminals themselves. By “virtual”, it is meant that when the channel conditions of the current sector selected by the mobile terminal are no longer satisfactory to the mobile terminal, the mobile terminal itself selects another sector by pointing its DRC towards a new sector. Queued data in the old sector is either retrieved by the new sector or flushed and retransmitted to the new sector. Therefore, there is no current mechanism within the CDMA2000 network for the network to initiate a handoff to another sector or HDR base station based on load conditions.